1. Field of the Invention
The present invention relates to a plastic spectacles lens containing an organic dye instead of a neodymium compound having optical absorbing performance. The plastic spectacles lens of the present invention exhibits optical transmission equivalent to a plastic spectacles lens containing a neodymium compound.
2. Description of Related Art
Reducing a displeasing feeling relevant to dazzle by visible rays, an indistinctness of contrast, visual fatigue, and the like, is one application object of a spectacles lens. As one of the measures, a spectacles lens is provided with a dazzle-preventing function. A principal measure is to shade dazzling wavelength rays as selectively as possible. In practice, a spectacles lens containing a neodymium compound which can highly selectively absorb visible rays near a wavelength of 585 nm is used. Such a spectacles lens can effectively prevent dazzle.
This technique is based on the principle of providing the spectacles lens with an appropriate light blocking effect. Excessive shading or blocking rays with inappropriate wavelength may, however, unnecessarily impair visibility which is the original objective of the spectacles lens. Thus, a technique capable of maintaining visibility as satisfactory as possible, and, at the same time, providing the spectacles lens with an appropriate light blocking effect is desired.
A method of adding a rare earth metal compound, particularly a neodymium compound, with an objective of providing a dazzle-preventing effect and increasing contrast, is widely used, as mentioned above. It is worth noting that a rare earth metal compound has a very sharp peak in the absorption spectrum in the wavelength band of the visible ray region, that is, the rare earth metal compound has a narrow absorption wavelength region and is wavelength-selective. The absorption peak of a neodymium compound, for example, near 585 nm wavelength is also very sharp.
This characteristic of possessing a sharp absorption peak contributes to the high optical transmission in the wavelength band required for visibility and also to selective absorption of rays in the wavelength band exhibiting a dazzling effect. Thus, the neodymium compound provides the spectacles lens with both a dazzle-preventing effect- and visibility. The glass containing a neodymium compound has extremely desirable properties as a dazzle-preventing spectacles lens.
A method of adding a rare earth metal oxide to a glass lens as disclosed in Patent Document 1 has been generally employed for manufacturing a rare earth metal compound-containing lens. In accordance with the trend of switching the lens material from glass to plastic, a plastic lens containing a specific organic rare earth metal complex has been developed.
However, the method of incorporating an organic rare earth metal complex into a plastic lens material leaves many problems to be solved. In the first place, selection of the organic moiety in the organic rare earth metal complex is considerably restricted according to the lens material. Only an expensive organic rare earth metal complex can be used in many cases. In particular, in the case of a thiourethane lens, a common organic rare earth metal complex can be used only with difficulty due to poor solubility and dispersibility in the resin, undesirable reactivity with the lens resin, and poor storage stability under ordinary conditions. Only a very specific organic rare earth metal complex as in Patent Document 2 has been disclosed, but the disclosed technology still leaves many problems to be solved.
In the second place, an organic rare earth metal complex must be added in an amount usually of about 5 wt % in order to achieve low light transmission rate (a high light blocking effect) to the light in the above-mentioned wavelength band. It is necessary to use a large amount of an expensive organic rare earth metal complex, but on the other hand, the amount of organic rare earth metal complex must be controlled so as not to impair the mechanical characteristics of the lens.
In view of this technological background, various methods of providing a plastic lens with a function of shading the light with a specific wavelength band as selectively as possible have been disclosed. For example, Patent Document 3 discloses a method of dying the lens by immersing the lens in an aqueous solution of a dye after molding, in order to provide dazzle-preventive properties, and Patent Documents 4, 5, and 6 disclose a method of curing a monomer after adding a cobalt compound or a specific organic dye to the monomer.
However, the dyes or compounds added in the method of Patent Documents 3 to have an absorption band different from the wavelength band of the neodymium compound. In addition, some compounds have an extremely wide absorption band that unnecessarily blocks light in other visible regions in order to attain an effective dazzle-preventing effect, with a result of undue sacrifice of visibility.
Patent Document 6 describes a lens with minimum optical transrmission close to 550 to 630 nm prepared by introducing a dye by a staining technique as a comparative example to the lens containing a neodymium compound. A defect of the technique of unduly decreasing clarity as compared with the case in which a neodymium compound is used is indicated.
Patent Document 7 discloses dazzle-preventing spectacles lens containing an organic dye which has a maximum absorption index near 575 nm and a comparatively sharp peak width. The lens is drastically improved in the absorption wavelength region, as well as in the above-mentioned region width, over the lenses disclosed in Patent Documents 3 to 6.
However, when the target level is achieved by the use of a neodymium compound, the absorption band narrowness is particularly insufficient not only in terms of providing the lens with brightness, but also in terms of providing the lens with various color tones such as a gray tone and a brown tone commonly used in commercial sunglasses. Thus, the proposed organic dyes have a problem of imposing a certain restriction to the commonly used technique of providing the lens with the target color tone by a combined use of other dyes.
In sunglasses or dark spectacles lenses to protect the eyes from environment light and to reduce a displeasing feeling, lenses with various color tones are used according to the use environment and user's demands. The technique of mixing two or more dyes to obtain the target color tone is usually employed. When the target color tone is produced by mixing dyes while maintaining the selective light absorption characteristics in a specific visible ray wavelength region as in the case of the present invention, a light absorption factor in a wavelength band other than the required selective light wavelength is preferably as small as possible, that is, the light absorption peak width is preferably as sharp as possible, in order to ensure a simple combination of dyes, a wide target color tone, and a color tone with little dullness.
Thus, it can be understood that a drawback common to the methods of staining a plastic lens with an organic dye replacing a neodymium compound is the extremely wide absorption band, and for this reason, it has been difficult to provide a lens with a superior dazzle-preventing effect and visibility, and excellent color-tone setting properties comparative to a rare earth metal.
[Patent Document 1] Japanese Patent No. 3044017
[Patent Document 2] WO 96/00247
[Patent Document 3] Examined Patent Publication No. 53-39910
[Patent Document 4] Japanese Patent Application Laid-open No. 5-5860
[Patent Document 5] Japanese Patent Application Laid-open No. 5-45610
[Patent Document 6] Japanese Patent Application Laid-open No. 2-254401
[Patent Document 7] Japanese Patent No. 3718185